1. Field of the Invention
The present invention relates to a cable test bench for testing a test cable to establish service life, replacement age, number of flex cycles, and/or winding behavior, having a deflection system comprising at least one deflector roll to deflect the test cable, one test cable drive to wind and unwind the test cable via the deflection system, and one test load to load the test cable.
2. Description of Related Art
Cables in safety applications, such as steel and fiber ropes of hoisting machines such as cranes, must be tested under test bench conditions to establish their service life, their replacement age, and their allowed number of flex cycles, in order to be able to make reliable determinations of how long the affected cable may be used in operation. For this purpose, cable test stands are typically used wherein a cable being tested is guided around at least one deflector roll under a defined load, in order to simulate a corresponding flexing process under load. Multiple cable rolls are typically used for this procedure in order to simulate opposing flexing processes, wherein the test load is hoisted and lowered in multiple test cycles, such that the test cable is subjected to corresponding flex cycles in a repeating winding and unwinding. Conventional cable test benches in this case regularly determine the number of cable flex cycles before replacement age and up to the breaking of the cable resulting from alternating movement of the cable over the at least one cable roll, with modified tensile force on the cable—for example by suspending various different test loads—or with smaller or larger ratios of the diameter of the cable roll to the diameter of the cable. In this way, it is possible to test cables made of different materials and having different braid pattern, and to determine the replacement age and the service life together with the number of flex cycles.
To date, in order to obtain not only results on the simple number of flex cycles, but also to arrive at results on the service life of a cable used in a wire rope drive system having a cable drum and cable rolls—as in the case of crane hoists or crane boom control systems, for example—cable test stands have been used which consist of a tower with trusses, or two towers with a connector, wherein a cable winch is usually arranged at the foot of the tower, from which the test cable is guided to the top of the tower, the trusses, or the center of the connector via multiple deflector rolls to a load hook reeved with one or multiple passes. A test load is attached to the load hook, and the hoisting and lower thereof creates a test cycle with a constant load. In order to prevent the load from falling if the cable breaks, the load can be guided on perpendicular rails which have a fall arrestor similar to that of passenger elevators. However, after a break of the cable, it is not easy to reset the test stand for further use, and sometimes requires a great deal of time.
A further disadvantage of cable test stands to date is that they only emulate the load cycles which occur in cranes and hoisting machines to a limited degree. The cable test stands typically only have the chance to carry out a test cycle with hoisting and lowering using the particular test load suspended from the stand. As a result, the cable has substantially the same tensile load both during hoisting and lowering, which in this case only varies as a result of differences in the degree of efficiency. However, this does not correspond to the actual application of a cable in a cable drive system, for example in a lifting unit of hoisting machines. By way of example, cranes typically hoist a load, set down the load once hoisted, and move on to the next load with still raised with no load, and/or are lowered with no load. In this case, a complete load cycle on the lifting gear is typically approximately 50% hoisting under load, and 50% lowering without load. According to the application, however, lifting gear load cycles can occur with the opposite load profile, wherein the load is received at the maximum hoisting height, or the load is released in the lowered position—as in the case of tunnel construction sites, for example. In this case, the lifting gear load cycle typically comprises 50% lowering under load, and 50% hoisting without load.
These load cycles occurring in practice in cranes or other hoisting machines can only be insufficiently emulated by cable test stands used to date, because it is generally not possible to set down the load or pick up the load after the hoisting path has been traveled. However, this would be important for determining the cable service life in a manner appropriate to actual practice.
In addition, cable test stands to date only insufficiently determine the winding behavior of the cable as appropriate to actual practice. According to experience, if the test load is hoisted and lower under constant cable tension, and accordingly the test cable is wound and unwound under a constant load, the test cable demonstrates good winding behavior. However, in practice, the winding behavior of the cable is altered when the cable is wound without a load as a result of the load being set down at a height, and/or when the cable is unwound without a last as a result of the load being set down after being lowered. In addition, such load cycles in the winding and unwinding of the cable also influence the life cycle of the cable, which cannot be sufficiently emulated by cable test benches to date. The winding behavior under alternating cable tension is also specifically of interest when windings occur in multiple layers—meaning that the cable is not wound only in one layer, but is wound around the winch roll in multiple layers—because in this case the cable is subjected to loads in a different manner as a result of cable layers lying one on top of the other. It has also not been possible to reproduce this in test stands to date.
The problem addressed by the present invention is therefore that of creating an improved cable test stand of the type named above which avoids the disadvantages of the prior art and develops the same in an advantageous manner. In particular, the loads which actually occur in cables of hoisting machines such as cranes should be emulated in a manner which is appropriate to actual practice, without the need for this to be achieved at the cost of complex handing to carry out the test cycles, such as suspending and un-hanging additional test loads, and the cable test stand should have a simple construction.